Rogue

The worst enemy CI5 ever faces is one of its own. Barry Martin was there at the start, a founder-member alongside Cowley, and he taught Bodie and Doyle unarmed combat, which means he knows exactly how they fight. Now he has turned rogue for money. His first betrayal is the worst kind: he hands a witness, kept under wraps for an upcoming drugs trial, straight to the killers. Then he shoots a man dead and puts a bullet in Cowley, who ends up in hospital.

What follows is the show's favourite kind of chase, two men hunting someone trained to the same standard they were. Martin knows every move they might make, because he taught some of those moves. The pursuit runs through the city and ends in an underground car park, with the series' usual resolution: a final shoot-out between men who were once on the same side. Cowley, laid up in hospital, can only listen to the chase from his bed, which for him is the worst seat in the house. There is a melancholy to it that the show does not labour, the sense of a family settling an account with a prodigal. The car park is a fitting stage for the last act, all concrete and bad light.

Brian Clemens and Dennis Spooner wrote it, and Ray Austin directed. Glyn Owen plays Martin with the right weary authority, a man who knows exactly what he has thrown away. Pamela Stephenson is Maggie Briggs, Tony Steedman is Paul Culbertson, Neil Hallett is David Hunter, Robert Gillespie is Steve Ballard, Teddy Green is a mortuary doctor and Diana Weston is Ruth.

It is a simple story told well: the best-trained man in the department turns on it, and the department has to bring him down. The tragedy is that everyone involved knows exactly how good he was.